Flexible, stretchable electronics that can change size and shape dynamically are poised to open doors to innovation

Medical implants of the future may feature reconfigurable electronic platforms that can morph in shape and size dynamically as bodies change or transform to relocate from one area to monitor another within our bodies. In Applied Physics Letters, a group of researchers reports a silicon honeycomb-serpentine reconfigurable electronic platform that can dynamically morph into three different shapes: quatrefoils (four lobes), stars and irregular ones. This image shows: (a) the serpentine-honeycomb reconfigurable platform. (b) The design with the eight reconfiguring nodes highlighted. (c) The irregular configuration. (d) The quatrefoil configuration. (e) The star configuration. CREDIT Muhammad Hussain

Reconfigurable electronics show promise for wearable, implantable devices

Medical implants of the future may feature reconfigurable electronic platforms that can morph in shape and size dynamically as bodies change or transform to relocate from one area to monitor another within our bodies.

In Applied Physics Letters, from AIP Publishing, a group of researchers from King Abdullah University of Science and Technology and University of California, Berkeley reports a silicon honeycomb-serpentine reconfigurable electronic platform that can dynamically morph into three different shapes: quatrefoils (four lobes), stars and irregular ones.

“Quatrefoils can be used for rectangular object-based operation, while stars are for more intricate architectures, and irregular-shaped ones are specifically for implanted bioelectronics,” said Muhammad Hussain, co-author and a visiting professor at the University of California, Berkeley.

With their work, the researchers are introducing a new branch of flexible, stretchable electronics — opening the door to new engineering challenges and providing opportunities for innovation in biomedical technologies that can be used for drug delivery, health monitoring, diagnosis, therapeutic healing, implants and soft robotics.

Inspiration for the group’s honeycomb-shaped platform comes from nature. “Think of how flowers bloom. Based on the same principle, we gathered many videos of flowers blossoming, analyzed their geometric pattern and used them for our first set of designs,” Hussain said. “In particular, we analyzed their stress distribution in an iterative manner, taking design architecture, materials and their properties into consideration. It’s a tedious process to reach the optimal balance, but this is where engineering helps.”

Reconfigurable electronic platforms are designed to undergo physical deformation, such as stretching, bending, folding or twisting to morph into another shape. “Imagine that a lab-on-chip platform is implanted within your body to monitor the growth of a tumor in the shoulder area,” said Hussain. “While it is implanted, if we observe some abnormality in lung function, a platform that is equipped enough can change its shape and size, and relocate or expand to go monitor lung function.”

Another idea the researchers are actively pursuing is a wearable heart sleeve to monitor heart activity with the ability to mechanically pump the heart by repeated expansion and contraction when needed.

“We still have a long way to go to integrate soft robotics with embedded high-performance flexible complementary metal-oxide semiconductor (CMOS) electronics on a variety of reconfigurable electronic platforms, which will be of immense importance,” Hussain said. “It offers wonderful engineering challenges, requires true multidisciplinary efforts and has the ability to bind a variety of disciplines into applications that are simply not possible with the existing electronics infrastructure.”

Learn more: Reconfigurable electronics show promise for wearable, implantable devices

 

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Printing flexible electronics on almost anything using a new heat-free technique

Martin Thuo and his research group have developed heat-free technology that can print conductive, metallic lines and traces on just about anything, including a rose petal. Photo courtesy of Martin Thuo.

Martin Thuo of Iowa State University and the Ames Laboratory clicked through the photo gallery for one of his research projects.

How about this one? There was a rose with metal traces printed on a delicate petal.

Or this? A curled sheet of paper with a flexible, programmable LED display.

Maybe this? A gelatin cylinder with metal traces printed across the top.

All those photos showed the latest application of undercooled metal technology developed by Thuo and his research group. The technology features liquid metal (in this case Field’s metal, an alloy of bismuth, indium and tin) trapped below its melting point in polished, oxide shells, creating particles about 10 millionths of a meter across.

When the shells are broken – with mechanical pressure or chemical dissolving – the metal inside flows and solidifies, creating a heat-free weld or, in this case, printing conductive, metallic lines and traces on all kinds of materials, everything from a concrete wall to a leaf.

That could have all kinds of applications, including sensors to measure the structural integrity of a building or the growth of crops. The technology was also tested in paper-based remote controls that read changes in electrical currents when the paper is curved. Engineers also tested the technology by making electrical contacts for solar cells and by screen printing conductive lines on gelatin, a model for soft biological tissues, including the brain.

“This work reports heat-free, ambient fabrication of metallic conductive interconnects and traces on all types of substrates,” Thuo and a team of researchers wrote in a paper describing the technology recently published online by the journal Advanced Functional Materials.

Thuo – an assistant professor of materials science and engineering at Iowa State, an associate of the U.S. Department of Energy’s Ames Laboratory and a co-founder of the Ames startup SAFI-Tech Inc. that’s commercializing the liquid-metal particles – is the lead author. Co-authors are Andrew Martin, a former undergraduate in Thuo’s lab and now an Iowa State doctoral student in materials science and engineering; Boyce Chang, a postdoctoral fellow at the University of California, Berkeley, who earned his doctoral degree at Iowa State; Zachariah Martin, Dipak Paramanik and Ian Tevis, of SAFI-Tech; Christophe Frankiewicz, a co-founder of Sep-All in Ames and a former Iowa State postdoctoral research associate; and Souvik Kundu, an Iowa State graduate student in electrical and computer engineering.

The project was supported by university startup funds to establish Thuo’s research lab at Iowa State, Thuo’s Black & Veatch faculty fellowship and a National Science Foundation Small Business Innovation Research grant.

Thuo said he launched the project three years ago as a teaching exercise.

“I started this with undergraduate students,” he said. “I thought it would be fun to get students to make something like this. It’s a really beneficial teaching tool because you don’t need to solve 2 million equations to do sophisticated science.”

And once students learned to use a few metal-processing tools, they started solving some of the technical challenges of flexible, metal electronics.

“The students discovered ways of dealing with metal and that blossomed into a million ideas,” Thuo said. “And now we can’t stop.”

And so the researchers have learned how to effectively bond metal traces to everything from water-repelling rose petals to watery gelatin. Based on what they now know, Thuo said it would be easy for them to print metallic traces on ice cubes or biological tissue.

All the experiments “highlight the versatility of this approach,” the researchers wrote in their paper, “allowing a multitude of conductive products to be fabricated without damaging the base material.”

Learn more: Self-sterilizing polymer proves effective against drug-resistant pathogens

 

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Opening up the possibility of commercializing inexpensive electronic devices based on a variety of 2-D materials

Researchers in MIT’s Department of Mechanical Engineering have developed a technique to harvest 2-inch diameter wafers of 2-D material within just a few minutes.
Image: Peng Lin

Efficient method for making single-atom-thick, wafer-scale materials opens up opportunities in flexible electronics.

Since the 2003 discovery of the single-atom-thick carbon material known as graphene, there has been significant interest in other types of 2-D materials as well.

These materials could be stacked together like Lego bricks to form a range of devices with different functions, including operating as semiconductors. In this way, they could be used to create ultra-thin, flexible, transparent and wearable electronic devices.

However, separating a bulk crystal material into 2-D flakes for use in electronics has proven difficult to do on a commercial scale.

The existing process, in which individual flakes are split off from the bulk crystals by repeatedly stamping the crystals onto an adhesive tape, is unreliable and time-consuming, requiring many hours to harvest enough material and form a device.

Now researchers in the Department of Mechanical Engineering at MIT have developed a technique to harvest 2-inch diameter wafers of 2-D material within just a few minutes. They can then be stacked together to form an electronic device within an hour.

The technique, which they describe in a paper published in the journal Science, could open up the possibility of commercializing electronic devices based on a variety of 2-D materials, according to Jeehwan Kim, an associate professor in the Department of Mechanical Engineering, who led the research.

The paper’s co-first authors were Sanghoon Bae, who was involved in flexible device fabrication, and Jaewoo Shim, who worked on the stacking of the 2-D material monolayers. Both are postdocs in Kim’s group.

The paper’s co-authors also included students and postdocs from within Kim’s group, as well as collaborators at Georgia Tech, the University of Texas, Yonsei University in South Korea, and the University of Virginia. Sang-Hoon Bae, Jaewoo Shim, Wei Kong, and Doyoon Lee in Kim’s research group equally contributed to this work.

“We have shown that we can do monolayer-by-monolayer isolation of 2-D materials at the wafer scale,” Kim says. “Secondly, we have demonstrated a way to easily stack up these wafer-scale monolayers of 2-D material.”

The researchers first grew a thick stack of 2-D material on top of a sapphire wafer. They then applied a 600-nanometer-thick nickel film to the top of the stack.

Since 2-D materials adhere much more strongly to nickel than to sapphire, lifting off this film allowed the researchers to separate the entire stack from the wafer.

What’s more, the adhesion between the nickel and the individual layers of 2-D material is also greater than that between each of the layers themselves.

As a result, when a second nickel film was then added to the bottom of the stack, the researchers were able to peel off individual, single-atom thick monolayers of 2-D material.

That is because peeling off the first nickel film generates cracks in the material that propagate right through to the bottom of the stack, Kim says.

Once the first monolayer collected by the nickel film has been transferred to a substrate, the process can be repeated for each layer.

“We use very simple mechanics, and by using this controlled crack propagation concept we are able to isolate monolayer 2-D material at the wafer scale,” he says.

The universal technique can be used with a range of different 2-D materials, including hexagonal boron nitride, tungsten disulfide, and molybdenum disulfide.

In this way it can be used to produce different types of monolayer 2-D materials, such as semiconductors, metals, and insulators, which can then be stacked together to form the 2-D heterostructures needed for an electronic device.

“If you fabricate electronic and photonic devices using 2-D materials, the devices will be just a few monolayers thick,” Kim says. “They will be extremely flexible, and can be stamped on to anything,” he says.

The process is fast and low-cost, making it suitable for commercial operations, he adds.

The researchers have also demonstrated the technique by successfully fabricating arrays of field-effect transistors at the wafer scale, with a thickness of just a few atoms.

“The work has a lot of potential to bring 2-D materials and their heterostructures towards real-world applications,” says Philip Kim, a professor of physics at Harvard University, who was not involved in the research.

The researchers are now planning to apply the technique to develop a range of electronic devices, including a nonvolatile memory array and flexible devices that can be worn on the skin.

They are also interested in applying the technique to develop devices for use in the “internet of things,” Kim says.

“All you need to do is grow these thick 2-D materials, then isolate them in monolayers and stack them up. So it is extremely cheap — much cheaper than the existing semiconductor process. This means it will bring laboratory-level 2-D materials into manufacturing for commercialization,” Kim says.

“That makes it perfect for IoT networks, because if you were to use conventional semiconductors for the sensing systems it would be expensive.”

Learn more: Researchers quickly harvest 2-D materials, bringing them closer to commercialization

 

 

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Stopping epileptic seizures with an electronic device planted in the brain

via University of Cambridge

Researchers have successfully demonstrated how an electronic device implanted directly into the brain can detect, stop and even prevent epileptic seizures.

These thin, organic films do minimal damage in the brain, and their electrical properties are well-suited for these types of applications.

George Malliaras

The researchers, from the University of Cambridge, the École Nationale Supérieure des Mines and INSERM in France, implanted the device into the brains of mice, and when the first signals of a seizure were detected, delivered a native brain chemical which stopped the seizure from progressing. The results, reported in the journal Science Advances, could also be applied to other conditions including brain tumours and Parkinson’s disease.

The work represents another advance in the development of soft, flexible electronics that interface well with human tissue. “These thin, organic films do minimal damage in the brain, and their electrical properties are well-suited for these types of applications,” said Professor George Malliaras, the Prince Philip Professor of Technology in Cambridge’s Department of Engineering, who led the research.

While there are many different types of seizures, in most patients with epilepsy, neurons in the brain start firing and signal to neighbouring neurons to fire as well, in a snowball effect that can affect consciousness or motor control. Epilepsy is most commonly treated with anti-epileptic drugs, but these drugs often have serious side effects and they do not prevent seizures in three out of 10 patients.

In the current work, the researchers used a neurotransmitter which acts as the ‘brake’ at the source of the seizure, essentially signalling to the neurons to stop firing and end the seizure. The drug is delivered to the affected region of the brain by a neural probe incorporating a tiny ion pump and electrodes to monitor neural activity.

When the neural signal of a seizure is detected by the electrodes, the ion pump is activated, creating an electric field that moves the drug across an ion exchange membrane and out of the device, a process known as electrophoresis. The amount of drug can be controlled by tuning the strength of the electric field.

“In addition to being able to control exactly when and how much drug is delivered, what is special about this approach is that the drugs come out of the device without any solvent,” said lead author Dr Christopher Proctor, a postdoctoral researcher in the Department of Engineering. “This prevents damage to the surrounding tissue and allows the drugs to interact with the cells immediately outside the device.”

The researchers found that seizures could be prevented with relatively small doses of drug representing less than 1% of the total amount of drug loaded into the device. This means the device should be able to operate for extended periods without needing to be refilled. They also found evidence that the delivered drug, which was in fact a neurotransmitter that is native to the body, was taken up by natural processes in the brain within minutes which, the researchers say, should help reduce side effects from the treatment.

Although early results are promising, the potential treatment would not be available for humans for several years. The researchers next plan to study the longer-term effects of the device in mice.

Malliaras is establishing a new facility at Cambridge which will be able to prototype these specialised devices, which could be used for a range of conditions. Although the device was tested in an animal model of epilepsy, the same technology could potentially be used for other neurological conditions, including the treatment of brain tumours and Parkinson’s disease.

Learn more: Electronic device implanted in the brain could stop seizures

 

 

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New metal printing technology for low-cost, flexible and stretchable electronics

This prototype demonstrates the potential of the new technique for printing flexible, stretchable circuits.

Researchers from North Carolina State University have developed a new technique for directly printing metal circuits, creating flexible, stretchable electronics. The technique can use multiple metals and substrates and is compatible with existing manufacturing systems that employ direct printing technologies.

“Flexible electronics hold promise for use in many fields, but there are significant manufacturing costs involved – which poses a challenge in making them practical for commercial use,” says Jingyan Dong, corresponding author of a paper on the work and an associate professor in NC State’s Edward P. Fitts Department of Industrial & Systems Engineering.

“Our approach should reduce cost and offer an efficient means of producing circuits with high resolution, making them viable for integrating into commercial devices,” Dong says.

The technique uses existing electrohydrodynamic printing technology, which is already used in many manufacturing processes that use functional inks. But instead of ink, Dong’s team uses molten metal alloys with melting points as low as 60 degrees Celsius. The researchers have demonstrated their technique using three different alloys, printing on four different substrates: one glass, one paper and two stretchable polymers.

“This is direct printing,” Dong says. “There is no mask, no etching and no molds, making the process much more straightforward.”

The researchers tested the resilience of the circuits on a polymer substrate and found that the circuit’s conductivity was unaffected even after being bent 1,000 times. The circuits were still electrically stable even when stretched to 70 percent of tensile strain.

The researchers also found that the circuits are capable of “healing” themselves if they are broken by being bent or stretched too far.

“Because of the low melting point, you can simply heat the affected area up to around 70 degrees Celsius and the metal flows back together, repairing the relevant damage,” Dong says.

The researchers demonstrated the functionality of the printing technique by creating a high-density touch sensor, fitting a 400-pixel array into one square centimeter.

“We’ve demonstrated the resilience and functionality of our approach, and we’re open to working with the industry sector to implement the technique in manufacturing wearable sensors or other electronic devices,” Dong says.

Learn more: Metal Printing Offers Low-Cost Way to Make Flexible, Stretchable Electronics

 

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